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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 192014
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
414 PM EDT SUN MAY 19 2013

.SYNOPSIS...
-- Changed Discussion --
AN UPPER LEVEL DISTURBANCE OVER THE AREA WILL DISSIPATE THROUGH
TUESDAY. ATLANTIC HIGH PRESSURE WILL THEN PREVAIL UNTIL LATE WEEK.
A COLD FRONT WILL DROP THROUGH THE AREA LATE FRIDAY INTO
SATURDAY...FOLLOWED BY HIGH PRESSURE THROUGH NEXT WEEKEND.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
-- Changed Discussion --
THIS AFTERNOON...ONGOING SHOWERS/THUNDERSTORMS CONTINUE WITH THE
BULK OF THE ACTIVITY ACROSS SOUTHEAST GA AND INTO SOUTHEAST SC ALONG
THE SAVANNAH RIVER. THE FOCUS FOR THE STRONGEST CONVECTION WILL
CONTINUE TO BE LOCATIONS CLOSER TO THE ALTAMAHA NEAR THE AXIS OF
BEST INSTABILITY AND WHERE THE BEST INSOLATION TOOK PLACE OVER THE
LAST FEW HOURS. STORMS ROUGHLY ALONG AND SOUTH OF I-16 MAY BRIEFLY
BECOME SEVERE WITH HAIL TO THE SIZE OF QUARTERS AND STRONG DAMAGING
WIND GUSTS. THE OVERALL SEVERE THREAT IS STILL LOW HOWEVER AND WILL
BE ISOLATED AT BEST.

TONIGHT...THE OVERALL SYNOPTIC SETUP WILL BE SIMILAR TO LAST NIGHT
WITH THE BAGGY MID-LEVEL DISTURBANCE POSITIONED TO THE NORTH AND
MOIST SOUTHERLY/SOUTHEASTERLY FLOW AROUND ATLANTIC HIGH PRESSURE AT
THE SURFACE. ONCE THE LINGERING EVENING STORMS DIMINISH WITH THE
LOSS OF AFTERNOON HEATING...THERE WILL BE A PERIOD OF MINIMAL PRECIP
COVERAGE UNTIL LATE TONIGHT. IN THE LATE NIGHT PERIOD...THE VARIOUS
HI-RES MODELS SHOW ANOTHER ROUND OF PRECIP MOVING ONSHORE FROM THE
ATLANTIC AND AFFECTING MAINLY THE SC COASTLINE. DEEP MOISTURE WITH
PWATS AROUND 1.7 INCHES AND SUBTLE CONVERGENCE WITHIN THE ONSHORE
SOUTHERLY FLOW WILL BE THE PRIMARY DRIVER. POPS FEATURE A WEST TO
EAST GRADIENT WITH SLIGHT CHANCES TO THE WEST AND HIGH CHANCES TO
THE EAST ACROSS CHARLESTON COUNTY. THE PRESENCE OF ELEVATED
INSTABILITY ABOVE THE NOCTURNAL INVERSION WILL KEEP THUNDER IN THE
FORECAST...BUT THE THREAT OF SEVERE WEATHER IS LOW. MORE OF A
CONCERN IS LOCALLY HEAVY RAINFALL...ESPECIALLY SINCE MANY LOCATIONS
ACROSS EASTERN CHARLESTON COUNTY SAW OVER 2 INCHES OF RAIN OVERNIGHT
LAST NIGHT. TEMPS WILL CONTINUE TO BE VERY MILD...ONLY FALLING INTO
THE UPPER 60S TO LOW 70S.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
-- Changed Discussion --
THE SHORTWAVE TROUGH ALOFT WILL BE SITUATED OVER THE REGION MONDAY
THEN WILL WEAKEN/UNRAVEL AND HIGHER PWATS SHOULD BE SHUNTED INLAND
TUESDAY AS HEIGHTS TEMPORARILY BUILD ALOFT AND ATLANTIC SURFACE HIGH
PRESSURE EXPANDS WESTWARD. THUS...EXPECT GREATER COVERAGE OF
SHOWERS/THUNDERSTORMS MONDAY AS COMPARED TO TUESDAY.
MONDAY...FORECASTS INDICATE HIGH CHANCE/LIKELY POPS AT MANY
LOCATIONS AWAY FROM THE BEACHES AROUND THE TIME OF MAX HEATING
MIDDAY UNTIL LATE AFTERNOON. THEN...CAPPED GREATEST POPS IN CHANCE
CATEGORY AWAY FROM THE BEACHES TUESDAY AFTERNOON. HOWEVER...IF THE
SHORTWAVE TROUGH PERSISTS INTACT LONGER THAN EXPECTED...TUESDAY
COULD BECOME SOMEWHAT MORE ACTIVE THAN INDICATED IN THIS FORECAST.

CANNOT RULE OUT BRIEF/PULSE SEVERE THUNDERSTORMS MONDAY OR TUESDAY
AFTERNOON...ESPECIALLY WHERE MESOSCALE BOUNDARY INTERACTIONS
OCCUR...BUT THE PRIMARY CONCERN WILL REMAIN LOCALLY HEAVY RAIN AS
PWATS REMAIN AROUND 1.75 INCHES ESPECIALLY MONDAY AND MULTICELL
CONVECTION EXHIBITS SLOW/SOMEWHAT ERRATIC PROPAGATION.
TUESDAY...PWATS SHOULD DECREASE TO SOME DEGREE.

WEDNESDAY...TEMPERATURES IN THE UPPER 80S TO AROUND 90F WILL BECOME
MORE COMMON AS THE ATLANTIC RIDGE PREVAILS. HOWEVER...THE SYNOPTIC
SCALE UPPER TROUGH APPROACHING FROM THE WEST WILL BEGIN TO IMPACT
THE REGION...SO AT LEAST SLIGHT CHANCE/CHANCE POPS FOR DIURNAL
SHOWERS/THUNDERSTORMS ARE JUSTIFIED DUE TO THE INFLUENCE OF THE SEA
BREEZE AND THE UPPER TROUGH.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
SIGNIFICANT MODEL DIFFERENCES APPEAR IN THE LONG TERM...MAINLY
REGARDING THE NEXT UPPER TROUGH THAT SHIFTS INTO THE EASTERN UNITED
STATES LATE IN THE WEEK. WE ARE TRENDING TOWARD THE ECMWF WHICH
MOVES THE UPPER TROUGH AND A COLD FRONT THROUGH THE AREA ON SATURDAY
WITH A DRY AND COOLER CANADIAN HIGH PRESSURE SYSTEM BUILDING IN
THEREAFTER. THUS WE ARE SHOWING DIURNAL...MAINLY SEABREEZE-DRIVEN
POPS THURSDAY AND FRIDAY...THEN DRY OVER THE WEEKEND.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
AT KSAV...THE MOST IMMEDIATE CONCERN IS DIRECT IMPACTS FROM
THUNDERSTORMS OVER THE NEXT 4-5 HOURS. CURRENTLY NUMEROUS SHOWERS
ARE DEVELOPING IN THE VICINITY AND A PREVAILING VCTS IS BEING
CARRIED IN THE FORECAST. STILL CAN/T SAY WITH TOTAL CONFIDENCE
THAT A THUNDERSTORM WILL MOVE DIRECTLY OVER THE AIRFIELD BUT I
HAVE ADDED A TEMPO FOR MVFR TSRA BETWEEN 20-22Z. THE MAIN IMPACT
WILL BE REDUCED VISIBILITIES IN HEAVY CONVECTIVE RAINS...BUT GUSTY
WINDS CANNOT BE RULED OUT. THEN OVERNIGHT...THE MAIN FORECAST
PROBLEM WILL BE THE DEVELOPMENT OF MVFR CEILINGS. I HAVE KEPT THE
FORECAST SCATTERED AT THE MVFR LEVEL...BUT SUBSEQUENT TAF
ISSUANCES MAY NEED TO GO PREVAILING MVFR.

AT KCHS...AFTERNOON SHOWER/THUNDERSTORM DEVELOPMENT OCCURRED NEAR
THE AIRFIELD AND THEN PUSHED INLAND. BASED ON EXTENSIVE CLOUD
COVER...THIS AREA SHOULD REMAIN MAINLY PRECIP FREE FOR THE
REMAINDER OF THE AFTERNOON SO I HAVE KEPT ANY MENTION OF
SHOWERS/STORMS OUT OF THE FORECAST. THE MAIN FORECAST ISSUE FOR
CHS OVERNIGHT IS THE DEVELOPMENT OF MVFR LEVEL CEILINGS AND
SHOWERS LATE. MODELS ONCE AGAIN HINT AT AN AXIS OF SHOWERS
STREAMING IN FROM OFFSHORE AND INTO MUCH OF CHARLESTON COUNTY LATE
TONIGHT. CONFIDENCE IN THE EXACT PLACEMENT OF THESE SHOWERS ISN/T
HIGH BUT COVERAGE SHOULD BE HIGH ENOUGH SUCH THAT A SHRA MENTION
IS WARRANTED. ALSO...THE FORECAST FEATURES PREVAILING MVFR
CEILINGS STARTING AT 10Z.

EXTENDED AVIATION...THE MAIN CONCERN WILL BE SPORADIC REDUCTIONS IN
CEILINGS AND VISIBILITIES...MAINLY ASSOCIATED WITH SCATTERED SHOWERS
AND THUNDERSTORMS THROUGH THE PERIOD. THE GREATEST CHANCES WILL BE
IN THE AFTERNOON HOURS SUNDAY THROUGH TUESDAY...ALTHOUGH EARLY
MORNING FLIGHT RESTRICTIONS CANNOT BE RULED OUT EACH DAY.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
TONIGHT...NO CHANGE TO THE SETUP WITH ATLANTIC HIGH PRESSURE DRIVING
PERSISTENT S TO SE FLOW. WIND SPEEDS WILL REMAIN AT OR BELOW 15 KTS
WITH SEAS 2-4 FT.

OFFSHORE HIGH PRESSURE WILL PERSIST THROUGH LATE WEEK...WITH
LOCALLY/BRIEFLY STRONGER ONSHORE WINDS AS HIGH AS 20 KT DUE TO THE
DIURNAL SEA BREEZE CIRCULATION EACH DAY. SEAS WILL AVERAGE 2 TO 4
FEET MUCH OF THE TIME. AHEAD OF AN APPROACHING COLD FRONT LATE IN
THE PERIOD...A TIGHTENING SURFACE PRESSURE GRADIENT COULD CONTRIBUTE
TO STRONGER WINDS AND BUILDING SEAS...AND THE PROBABILITY FOR LOW
END SMALL CRAFT ADVISORY CONDITIONS WILL INCREASE SOMEWHAT MID TO
LATE WEEK.
-- End Changed Discussion --

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

$$

SYNOPSIS...
NEAR TERM...BSH
SHORT TERM...SPR
LONG TERM...JRL
AVIATION...BSH/SPR
MARINE...BSH/SPR